Surface acoustic wave (SAW) devices are often used in filtering applications for high frequency signals. Given the inherent bulk and expense associated with SAW devices, efforts have been made to minimize the size and expense associated with the often-used devices.
SAW devices take advantage of elastic, or acoustic, waves that travel along an open and solid surface and through a vacuum or gas. Generally, a piezoelectric substrate provides the open and solid surface over which the elastic waves will propagate. The elastic waves are created upon exciting an interdigital transducer (IDT) by electrical signals, wherein in a two-port device the waves may be reciprocally received by another IDT. To maintain a free space on the surface of the piezoelectric substrate, the packages for SAW devices require a cavity. Creating a cavity in these SAW devices results in a component that is bulky and expensive to manufacture.
To address some of the issues with SAW devices, layer acoustic wave devices are proposed. Layer acoustic wave devices take advantage of elastic waves that travel in a layer confined by two surrounding mediums of different properties. With layer acoustic wave devices, the elastic wave need not travel along an open surface.
U.S. patent application number 2005/0099091 A1 to Mishima, entitled ELASTIC BOUNDARY WAVE DEVICE AND METHOD OF MANUFACTURING THE SAME (hereinafter “Mishima”), illustrates recent advances in devices with similar types of waves. Mishima creates a boundary wave device by assembling a first substrate with a first dielectric film, which covers IDTs that are formed on the first substrate. A second substrate is separately assembled, and includes a second dielectric film. The second substrate is then inverted and bonded together using a bonding process to form a junction between the first and second dielectric films. The second substrate is required in order to form a proper type of wave and to minimize leakage of the elastic wave to an outside surface of the resulting boundary wave device. Such leakage can interfere with other components and make the device less efficient. Although the suggestion by Mishima is an improvement over traditional SAW devices, the need to create different substrates and then bond the substrates together adds additional complexity and expense to the manufacturing process.
Accordingly, there is a need for an effective boundary wave device that can be efficiently manufactured. There is a further need to minimize the leakage of the elastic boundary waves to an outside surface of the resulting boundary wave device while avoiding the need to create separate substrates and employ bonding techniques to create the boundary wave device.